A study of ancient reef cores from the Indo-Pacific finds most reefs are likely to drown if sea-level rise exceeds historical growth limits, with knock-on risks for coastal communities and marine life.
If sea-level rise exceeds about 5.3 mm per year, most reefs are unlikely to build upward fast enough and will progressively submerge.
Reef drowning reduces the ability of reefs to block wave energy, raising erosion and flooding risks for low-lying coasts and islands.
Local actions such as controlling pollution and overfishing can help reef health but cannot replace the need to sharply reduce greenhouse gas emissions.
# What the study looked at
# Main finding The team concluded that under a high greenhouse gas emissions scenario, roughly 76% of the reef sites they examined will be unable to keep pace with projected sea-level rise. They identify a practical threshold: if sea level rises faster than about 5.3 mm per year, reef building is highly unlikely to match that rate. That threshold could be reached within decades under current emissions trajectories.
# What "reef drowning" means
# Consequences for coasts and communities Coral reefs reduce wave energy before it reaches the coast. If reefs become submerged and less structurally complex:
# Biological limits and species composition Not all corals contribute equally to reef building. Competitive coral species that dominated ancient reefs produced complex, rapidly built structures. Modern reefs are increasingly dominated by stress-tolerant, "weedy" corals that colonise disturbed areas quickly but build less structure. The shift in species composition reduces the reef's capacity to build upward even where local conditions are otherwise favorable.
# What helps, and what won't be enough Local measures — reducing pollution, limiting overfishing, and managing direct stressors — can maintain healthier, faster-growing reefs in some places. Those actions improve resilience and may buy time for reefs that are near the growth threshold. However, local management cannot compensate for sea-level rise that outpaces the corals' biological growth limits. The study concludes that substantial cuts in greenhouse gas emissions combined with local protection strategies are necessary to keep many reefs functioning.
# Bottom line The long-term reef record shows corals have historically adjusted to changing seas, but there are biological and structural limits to how fast a reef can grow. Under high-emissions scenarios, many Indo-Pacific reefs are at significant risk of drowning, with direct implications for coastal protection, livelihoods, and biodiversity.
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